Reaction Rates

Collision Theory  In order for reactions to occur, particles must collide  If collisions are too gentle, no reaction occurs  If collisions do not occur at the correct angle, no reaction occurs

Activation Energy  In order for reaction to occur, the old bonds of the substances must be broken before new bonds can form  Breaking the bonds is always endothermic while forming new bonds is exothermic  Even though an overall reaction is exothermic, it may require an initial input of energy to get the bonds broken – called activation energy (E a )

Activated Complex  An intermediate structure that atoms are in while breaking old bonds and making new ones

Energy Reaction coordinate Reactants Products

Energy Reaction coordinate Reactants Products Activation Energy (E a ) - Minimum energy to make the reaction happen

Energy Reaction coordinate Reactants Products Activated Complex or Transition State

Energy Reaction coordinate Reactants Products Overall energy change (  H)

Reaction Rate  Speed of a reaction  Measured by the change in concentration of reactants or products over time  As the reaction proceeds the concentration of reactants will decrease and the concentration of products will increase

Factors Affecting Reaction Rate  Changing conditions may affect the collision frequency or collision efficiency and this will affect the speed of the reaction  Five important factors influence the rate

1) Nature of Reactants – some substances are more reactive 2) Surface area – greater surface area faster reaction 3) Concentration – greater concentration, faster the reaction 4) Temperature – greater temp, faster reaction

5) Catalyst Substance not part of the reaction but makes the reaction faster by lowering the activation energy

Energy Reaction coordinate Reactants Products